Frequency conversion circuit using common local synthesizer

Abstract

A radio for use in microwave datalink applications in which a common local oscillator is used for both a final radio frequency (RF) up-converter stage and an initial RF down converter stage. The frequency of the common local oscillator corresponds to an integer multiple of a local oscillator needed for an earlier up-converter or later down converter stage. The circuit can be used to provide a radio frequency carrier in a 30 GHz band using Coaxial Resonator Oscillators (CRO's) that lend themselves to a planar microstrip circuit implementation.

Description

BACKGROUND OF THE INVENTION[0001]A number of access technologies are presently available for wireless data connectivity. These wireless access products include Wireless Local Loop (WLL), Fixed Wireless Access (FWA), Cellular Packet Data (CDPD), Wireless Local Area Network (WLAN), narrow aperture satellite technologies, Local Multipoint Distribution Service (LMDS), and Multipoint Distribution Service (MMDS). A range of data transfer speeds are supported with these technologies, including multiple or fractional T1 / E1 type, asynchronous transfer mode (ATM), digital video, plain old telephone service (POTS), and other types of digital signaling connections.[0002]Of chief interest to the present invention are broadband microwave communications systems, such as local multipoint distribution services (LMDS). Now available in the United States and in other countries, LMDS provides fast, flexible and economical broadband wireless connectivity, with line of sight coverage over a distance rang...

AI Technical Summary

Benefits of technology

[0009]The present invention is a radio for use in microwave data link applications in which a common local oscillator signal is used for both a final up-converter stage and an initial down-converter stage. The frequency of the common local oscillator is also chosen to correspond to an integer multiple of a needed local oscillator frequency for an earlier up-converter stage or a later down-converter stage. The required carrier frequency for the other leg, that is, namely, the corresponding down-converter or up-converter carrier, can then be provided by a local oscillator circuit that provides a multiplication factor needed to separate the up and downstream bands with a sufficient guard band at the cable side. This frequency converter design allows an all microstrip implementation and does not require high Q filters which would otherwise necessitate using waveguide components.

Problems solved by technology

Depending upon the specific details of frequency allocations for upstream and downstream channels, the design of the solid state circuits can therefore present certain challenges.

This type of filter represents large size, high cost and, depending on the precise frequency band plan, its loss can become significant when very narrow bandwidths are required.

However, the high-Q, narrowband characteristic of the waveguide filter cannot be practically duplicated in other circuit technologies.

While a microstrip circuit approach would add the complexity of additional frequency conversion stages, it would have a cost and size advantage over circuits employing waveguide.

Phase Locked Dielectric Resonator Oscillators (PLDRO's) provide excellent phase noise but are relatively high cost and not suitable for integration directly on the planar microwave circuit.

However, the use of a lower frequency local oscillator requires careful planning of how the multiple frequency conversion stages are implemented.

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